The present invention relates to a treatment tool insertion channel of an endoscope.
In general, there are provided to an insertion part of an endoscope a flexible tube and a bendable part linked with a distal end of the flexible tube so as to be bent by a remote control operation. In addition, there are arranged over the entire length of an inner space of the flexible tube and bendable part a treatment tool insertion channel configured such that a treatment tool is inserted thereinto and ejected therefrom.
Further, the treatment tool insertion channel is configured with a front portion (supple portion) thereof that includes an entire part located inside the bendable part being more flexible than a rear portion thereof such that the bendable part can smoothly be bent with a smaller curvature radius by a larger angle than the flexible tube.
In this regard, however, when the supple portion is merely formed from a supple flexible inner tube, the supple portion can easily be buckled due to an operation of bending the bendable part. Meanwhile, when the supple portion is formed with a large wall thickness, other elements such as an optical fiber bundle to be incorporated in the insertion part have to be formed with a small cross-sectional area. Thereby, basic performance of the endoscope is inevitably sacrificed.
In order to solve the aforementioned problems, conventionally, a spiral groove is provided on an outer circumferential surface of the part of the supple portion inside the bendable part such that the treatment tool insertion channel can be bent by a small force. In addition, a metal coil with spring characteristics is wound along a bottom of the spiral groove such that the treatment tool insertion channel cannot be buckled even though the bendable part is repeatedly bent (for example, see Japanese Utility Model Provisional Publication No. HEI 6-41701).
Additional, according to another conventional treatment tool insertion channel, the metal coil, which is wound along the bottom on the spiral groove formed around the part of the supple portion inside the bendable part, is extended rearward, and is wound on an outer circumferential surface of the flexible inner tube over the entire length of the supple portion that includes even a rear-side part without the spiral groove formed therearound as well as the front-side part (the part inside the bendable part) with the spiral groove formed therearound (for example, see Japanese Utility Model Provisional Publication No. SHO 62-39706).
However, according to the treatment tool insertion channel that is configured with the metal coil being wound along the bottom of the spiral groove formed on the outer circumferential surface of the front-side part of the supple portion inside the bendable part, when the flexible tube at the rear of the bendable part is bent with a small curvature radius, a rear portion of the treatment tool insertion channel without the metal coil wound therearound might be buckled.
In the meantime, when the metal coil is wound even on the outer circumferential surface of the rear-side part without the spiral groove formed therearound, the outer diameter of the entire treatment tool insertion channel is significantly enlarged. Therefore, other elements such as the optical fiber bundle to be incorporated in the insertion part have to be formed with a small cross-sectional area, and the basic performance of the endoscope is thereby sacrificed.
Further, when the supple portion is configured more flexible than the flexible portion with the spiral groove being formed only around the supple portion, mechanical characteristics are significantly different between the supple portion and the flexible portion. Therefore, there are caused problems that it is difficult to adapt both of the supple portion and the flexible portion in optimum flexibility conditions such that the treatment tool insertion channel is not easily buckled even at a border portion between the supple portion and the flexible portion.